Refrigerating apparatus having a free piston compressor



A. N. ADDIE Feb. 26, 1957 REFRIGERATING APEARATUS HAVING A FREE PISTON COMPRESSOR Filed Jan. 20, 1956 INVENTOR.

i ALBERT N ADD/E BY A TTORNEY REFRIGERATING APPARATUS HAVING A FREE PISTON COMPRESSOR Albert N. Addie, La Grange Park, 111., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application January 20, 1956, Serial No. 560,339 4 Claims. (Cl. 62-136) This invention relates to refrigerating apparatus and more particularly to a cooling system in which a free piston compressor is used to compress air which is re-expanded to produce cooling.

It is an object of this invention to provide an improved system in which air used as the refrigerant is circulated through a closed path which includes means for removing moisture from the air.

These and other objects of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

in the drawings:

The sole figure in the drawing shows somewhat schematically the refrigerant circuit and the relationship between the free piston compressor and other elements used in the system.

nited States Patent feeds this portion of the air into the inlet 46 of the free piston engine 10.

As shown in the drawing, the combustion chamber of the free piston compressor is supplied with atmospheric air and the exhaust air leaves the free piston compressor through the line 48 which feeds the exhaust air into a single radial inflow exhaust gas turbine 50 used to drive the fan 52. The fan 52 circulates atmospheric air over the after-cooler 14, as shown. The compressor and turbine rotors shown would preferably be on the order of 5 to 6" in diameter and would run at approximately 46,000 R. P. M. The values given herein are for purposes of illustration only and may be varied to suit the needs of individual installations. Insofar as this invention is concerned, any type of free piston air compressor could be used, whereas it is preferred to use one of the general type more fully disclosed in the February 1951 issue of the magazine entitled Power, to which reference is hereby made for a more complete description of the compressor.

The free piston compressor shown is of the two-cycle, opposed piston, diesel cylinder type which includes an air compressor cylinder 60 and a cushion cylinder 62, as shown. The usual synchronizing linkage 64 connects the two piston assemblies, as shown. Fuel is injected into compressed air in the diesel, or combustion, cylinder 86 at 66 and the resulting burning causes the pistons 68 and 70 to move outwardly. The large piston 71 operating in the cylinder 60 compresses air and discharges it through the valve 72 into the air reservoir 74. Fresh air is sucked into the air compressor cylinder behind the inner face of the compressor piston 71 through the valve 76 and this Referring now to the drawing, wherein a preferred embodiment of the invention has been shown, reference numeral 10 generally designates a free piston compressor which supplies compressed air into the line 12 which conveys the compressed air into an after-cooler 14 wherein the air is preferably cooled to a temperature of approximately 110 F. The air leavingthe after-cooler 14 flows through a line 16 which leads to the first stage 18 of a two-stage radial inflow turbine generally designated by the reference character 20. The air leaves the first stage of the turbine 20 through the line 22 which leads to a conventional dehumidifier 24 wherein moisture is condensed out of the air so as to prevent icing in the second stage 25 of the two-stage turbine 20. The condensed moisture accumulates in the lower part of the dehumidifier 24 and is drained out therefrom through an outlet 26 controlled by a valve mechanism 23 in accordance with conventional dehumidifier practice. Insofar as the main aspects of the invention are concerned, any type of dehumidifier could be used for removing moisture from the air.

Power developed by the air expanding in the turbine 20 is used to drive a two-stage centrifugal compressor 30, as shown. A shaft 32 serves to convey power from the turbine 20 to the compressor 30. The air leaves the twostage turbine 26 through a line 34 which leads to the hollow walls 36 of the refrigerated space 38. In passing through the two-stage turbine 20, the air is expanded to atmospheric pressure and as a result thereof it will have had its temperature reduced to approximately -40 F. before entering the space 30. It should be noted that this cold, dry air is not discharged into the space 38 to be conditioned where it would tend to reabsorb moisture but is circulated through the hollow walls 36 surrounding the space to be cooled. Insulation (not shown) would be placed adjacent the outside surface of the hollow wall structure to reduce infiltration of heat from the outside. The air leaves the hollow walls 36 at approximately l0 F. through an outlet line 40, as shown. One portion of the air leaves the main line 40 through a branch line 42 which leads to the two-stage compressor and another portion of the air leaves through a branch line 44 which air serves as the scavenging air for the combustion chamber 86. The bounce piston 63 compresses air in the cushion cylinder portion 62. This stored energy, plus that of air trapped in compressor clearance volume, returns the pistons towards the center. Toward the end of the outward stroke, the diesel pistons 68 and 70 uncover the ports 82 and 84 in the wall of the main combustion chamber 86. The burned gas exhausts out of the port 34 and into the passage 48 which leads to the exhaust turbine 50. Air enters the compression chamber at 46 and enters the scavenging reservoir at 76. A valve allows air from the scavenging resewoir 92 to enter the diesel chamber 86 as the diesel pistons reach the outer end of their stroke. As the diesel pistons reach the outer end of their strokes, the pressure in the combustion cylinder has fallen and compressed cushion air in the cylinder 62, plus energy of air in the clearance volume, causes the pistons to move toward the center On the return stroke, the compressor cylinderrefills and air is pumped into the scavenging reservoir. As this takes place, a new air charge is compressed in the combustion cylinder.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is as follows:

1. In a cooling system for use in refrigerating air for railway cars and the like, a free piston air compressor, an after-cooler arranged to cool the compressed air discharged from said free piston compressor, a two-stage turbine, means for supplying the compressed air thus cooled into the first stage of said two-stage turbine so as to r partially re-expand said air, a dehumidifier, means for directing the air leaving said first stage of said turbine into said dehumidifier so as to remove moisture therefrom, means for directing air leaving said dehumidifier into the second stage of said turbine so as to further expand said air to a pressure corresponding substantially to atmospheric pressure, means forming a space to be cooled, said means including hollow walls, means directing said ex- 3 panded air through the hollow portion of said walls, a centrifugal compressor, means drivingly connecting said centrifugal compressor to said turbine, means feeding a portion of the air leaving said hollow walls to said centrifugal compressor, means conveying the compressed air leaving said centrifugal compressor to the inlet of said after-cooler, and means for conveying another portion of the air leaving said hollow walls to the inlet of said free piston compressor.

2. In a cooling system, a free piston compressor having an inlet for air to be compressed and havingan outlet for compressed air, an after-cooler arranged to remove heat from said compressed air, means to re-expand said cooled compressed air so as to further reduce the temperature thereof, said means to re-expand including means for removing moisture from the air, means including a second compressor utilizing the energy released upon reexpansion of said air for compressing additional air, means for circulating said re-expanded air in thermal exchange relationship with a space to be cooled and for thereafter circulating a first portion of said re-expanded air to the inlet of said free piston compressor and a second portion thereof to the inlet of said second compressor, and means for connecting the outlet of said second compressor to the inlet of said after-cooler.

3. In a system for use in refrigerating railway cars and the like, a free piston air compressor, an after-cooler arranged to cool the compressed air discharged from said free piston compressor, a two-stage turbine, means for supplying the compressed air thus cooled into the first stage of said two-stage turbine for partial re-expansion therein, a dehumidifier, means directing the air leaving said first stage of said turbine into said dehumidifier so as to remove moisture therefrom, means directing air leaving said dehumidifier into the second stage of said turbine so as to further expand said air to a pressure corresponding substanstially to atmospheric pressure, means forming a space to be cooled, said means including hollow walls through which said expanded air is circulated, a two-stage compressor, means drivingly connecting said two-stage compressor to said turbine, means feeding a portion of the air leaving said hollow walls to the inlet of said two-stage compressor, means conveying the compressed air leaving said two-stage compressor to the inlet of said after-cooler, means conveying another portion of the air leaving said hollow walls to the inlet of said free piston compressor, said free piston compressor having a combustion chamber provided with an exhaust port, fan means circulating air in thermal exchange relationship with said after-cooler, and an exhaust turbine arranged to drive said fan means, and means supplying air from said exhaust port to said exhaust turbine for driving the same.

4. In a cooling system using air as the refrigerant, a free piston compressor having an inlet for air to be compressed and having an outlet for compressed air, an aftercooler connected to said outlet and arranged to remove heat from the compressed air, means to re-expand the air leaving said after-cooler so as to reduce the temperature thereof, said means to re-expand including means for removing moisture from the air, means including a second compressor utilizing the energy released upon re-expansion of the air for compressing air, means circulating the re-expanded air in thermal exchange relationship with a space to be cooled and for thereafter circulating a first portion of said air to the inlet of said free piston compressor and a second portion of said air to the inlet of said second compressor, means connecting the outlet of said second compressor to the inlet of said after-cooler, means circulating another portion of said air to the inlet of said free piston compressor, said free piston compressor having a combustion chamber provided with an exhaust port, fan means for circulating air in thermal exchange relationship with said after-cooler, an exhaust turbine arranged to drive said fan means, and means for supplying air from said exhaust port to said exhaust turbine for driving the same,

References Cited in the file of this patent UNITED STATES PATENTS 1,535,848 Nicholson Apr. 28, 1925 1,545,587 Leblanc July 14, 1925 2,115,921 Steiner May 3, 1938 

